Oh, I used this and the performance and deduplication surprised me greatly in ReFS. I was using it as a place to store backups of my systems. The on disk vs the file size was so great that I had to rethink my offsite storage solutions. There was a recent article on here from a researcher at Microsoft on file size and deduplication.
Deduplication is awesome, it's really unfortunate how dangerous it is with things available on Linux. I've had ZFS corrupt itself twice and not after disabling it, on the same hardware. And btrfs died on me once - I'm not 100% sure it's exactly due to that, but there's a limit how much I'm willing to spend time copying terabytes.